The Pipe Flow (pfl) interface (), found under the Single-Phase Flow branch () when adding a physics interface, is used to compute the velocity and pressure fields in pipes and channels of different shapes. It approximates the pipe flow profiles flow by 1D assumptions in curve segments, or lines. These lines can be drawn in 2D or 3D and represent simplifications of hollow tubes. The interface is available in 3D on edges, and in 2D on boundaries.

When this physics interface is added, these default nodes are also added to the Model Builder — Fluid Properties, Pipe Properties, Pressure, Lossless Fitting and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and volume forces. You can also right-click Pipe Flow to select physics features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first physics interface in the model) is pfl.

Select the Enable physics symbols check box to enable the display of physics symbols. See Pipe Flow Physics Feature Symbols for information about available physics symbols.

Under Show or hide all physics symbols, click the Select All button, which displays all symbols in that physics interface by selecting all Show physics symbols check boxes in the Settings windows for the physics features that include symbols. Similarly, the Clear All button clears all Show physics symbols check boxes in the individual physics features.

Select a Fluid model — Newtonian (the default), Power Law, Bingham, or Herschel-Bulkley.

For Newtonian select Single phase (the default), Gas-Liquid, friction factor multiplier, or Gas-Liquid, effective Reynolds number.

When Gas-Liquid, friction factor multiplier or Gas-Liquid, effective Reynolds number are selected, the Phase Fractions node is automatically added as a default node. Selecting these options also enables the choice of Liquid material and Gas material for the Fluid Properties node.

For more information about the fluid models, see the section Theory for the Pipe Flow Interface.